Drinking water has been, and continues to be, heavily treated for bacteria and other microscopic organisms that may cause infection in humans and other animals subsequent to consumption. In order to disinfect water supplies, halogenated materials have been introduced therein that have proven more than adequate for such a purpose. Unfortunately, although such halogenated compounds (chlorinated and chloraminated types, primarily) exhibit excellent disinfection capabilities, when present within aqueous environments at certain pH levels these halogenated compounds may generate byproducts that may themselves create health concerns. The United States Environmental Protection Agency (USEPA) in fact regulates five specific types of haloacetic acids within drinking water, monochloroacetic acid, dichloroacetic acid, trichloroacetic acid, monobromoacetic acid, and dibromoacetic acid, as well as four types of trihalomethanes, chloroform, bromodichloromethane, dibromochloromethane, and bromoform. Removal of such compounds from drinking water is not possible as for typical chlorinated and brominated disinfecting compounds, at least not at the same reliability level as for the disinfecting agents. Thus, residual amounts may remain within treated water supplies that may require further removal processes to be undertaken. Of course, if the level of contamination is sufficiently low, initiation of such potentially expensive removal steps would be unwise from an economic perspective.
The USEPA currently has set a maximum contaminant level for the five haloacetic acids (collectively referred to as HAA5; four other haloacetic acids are currently not regulated by the USEPA, bromochloroacetic acid, bromodichloroacetic acid, dibromochloroacetic acid, and tribromoacetic acid; including these, the total haloacetic acid group is known as HAA9) at a total amount of 0.060 mg/L and for the trihalomethanes at 0.080 mg/L. It is thus important to reliably analyze and measure the total amount of such contaminants in order to determine if removal if necessary.
The USEPA has instituted its own testing methods for such a purpose. One, known as EPA 552.2, involves the liquid-liquid extraction of haloacetic acids from water sources into methyl-t-butyl ether, followed by derivatization with acidic methanol to form the corresponding haloacetic acid methyl esters. Analysis by gas chromatography-electron capture detection provides reliable measurements of the haloacetic acid amounts present within the subject water supply. The other, USEPA 552.3, is a derivative of the first with optimizations of acidic methanol neutralization procedures for improvement in brominated trihalogenated haloacetic acid species. These general processes have been found to have numerous drawbacks, however. For instance, injection port temperature can affect debromination of certain haloacetic acid species (particularly tribrominated types) that may lead to under-representation of the amount of such contaminants present within the tested water source. Likewise the water content of the methyl-t-butyl ether extract may decarboxylate the haloacetic acids, again leading to an under-reporting of the actual amounts present within the test sample. Furthermore, the involved processing needed to actually undergo such analysis makes an on-line protocol rather difficult to implement, particularly when hourly sampling is necessary. Other derivatization methods have been either followed or suggested for gas chromatography analyses of drinking water sources as well, including utilizing diazomethane, acidic ethanol, and aniline. Such reactant-based measurements, however, all suffer the same time and labor-intensive problems as with the two EPA test procedures noted above. As such, on-line analysis through these protocols are difficult, expensive, and labor intensive to implement.
The most common USEPA testing protocols for THMs include USEPA method 502.2 and 524.2. Both methods use purge and trap technology to volatilize the THMs from a drinking water sample onto an adsorbent trap that concentrates the THMs. The adsorbent trap is then rapidly heated to desorb the THMs onto the gas chromatography column for separation. USEPA 502.2 uses an electrolytic conductivity detector to determine THM concentrations and USEPA 524.2 uses a mass spectrometer. Both of these methods provide reliable measurements of THMs concentrations in drinking water. However, both methods are expensive and neither method can be considered portable.
Measurement at the source (i.e., within a water purification plant location) may be effective for system-wide average readings; however, in the large supplies of water at such locations, the chances of proper sampling to that effect may be suspect since the contaminants may be present in varied locations, rather than definitely mixed throughout the tested water supply itself. Additionally, testing may not uncover the actual level of residual haloacetic acid or trihalomethane disinfection byproducts prior to the water supply being disbursed to distant dispense sites (transfer pipes, homes, schools, businesses, etc.). In any event, there is a relatively new rule in place that requires utilities to provide evidence of compliance with haloacetic acid levels at multiple locations, rather than a straightforward system-wide average. Thus, since the above-described derivatization procedures with gas chromatography-electron capture detection analytical methods and purge and trap gas chromatography with either previously mentioned detector are not suitable for a uniform haloacetic acid or trihalomethane measurement scheme. There is thus a drive to implement remote testing via real-time, on-line methods for water supply HAA5, and, more importantly, for HAA9 contaminant level measurements, not to mention for the four trihalomethanes, too.
Such a desirable on-line procedure has been difficult to achieve, however, particularly as it pertains to the determination of not only the amount of haloacetic acid and/or trihalomethane species, but also the amount of each species present within the tested water source. High performance liquid chromatography, utilizing electrospray ionization-mass spectrometry or ultraviolet absorbance as the detector, has been attempted, as well as ion chromatography, with membrane-suppressed conductivity detection or, as well, ultraviolet absorbance detection. Other attempts with inductively coupled plasma-mass spectrometry and electrospray ionization-mass spectrometry coupled with ion chromatography have been followed as well for this same purpose. The detection level can be as low as 0.5 to less than 10 μg/L for HAA9 species, but only subsequent to sample preparations. The sensitivity and selectivity of ion chromatography and high performance liquid chromatography methods are easily sacrificed without the cumbersome preparations in place, therefore requiring operator intervention during analysis. Again, this issue leads to serious drawbacks when on-line implementation is attempted as well.
Another methodology that has proven effective to a degree is post-column reaction-ion chromatography. This has shown promise, but only in terms of quantifying bromate ion concentrations in drinking water samples at a single microgram per liter level. This dual selectivity form (separation by ion chromatography column as well as the selective reaction with the post-column reagent with the analyte) offers an advantageous test method over the others noted above, except for the presence of more common anions, specifically chloride, at much higher concentrations within the sampled drinking water supply (mg/L instead of μg/L). It was then undertaken to combine the separation capabilities of ion chromatography with the reaction of the haloacetic acid species with nicotinamide, followed by fluorescence detection to measure the individual and total HAA5 concentrations in drinking water at the single μg/L level. The problem with such a protocol, unfortunately, was that bromochloroacetic acid interfered with dichloro- and dibromo-acetic acid quantifications. Despite this problematic limitation, it was determined that fluorescence detection provided a much improved detection protocol in comparison with ultraviolet absorbance and mass spectrometry possibilities. Thus, although such a fluorescence method of detection, coupled with the post-column reaction (again with nicotinamide reagent) and ion chromatography, exhibited the best results in terms of an on-line test method for HAA5 drinking water contaminant measurement levels, there remained a definite need for improvements in total haloacetic acid measurements and identifications within such test samples. Gas chromatography-based analysis is typically used for THMs combined with multiple sample preparation techniques and different detectors. USEPA 502.2 and 524.2 have previously been discussed, but suffer from being expensive and not portable. Capillary membrane sampling-gas chromatography with electron capture detection has been previously used to monitor THMs on-line as well as the on-line, purge and trap-gas chromatograpy with dry electrolytic conductivity detection. The capillary membrane sampling—gas chromatography with electron capture detection uses a membrane device to pervaporate the THMs across a silicone rubber membrane into a stream of nitrogen, which is then separated by a gas chromatography and detected with electron capture detection. The on-line purge and trap—gas chromatography instrument uses a silicone rubber membrane in similar fashion as the capillary membrane sampling device, but the THMs are swept onto an adsorbent trap for concentration. The THMs are then desorbed, separated on a GC column and detected with a dry electrolytic conductivity detector. To date, however, there has not been an analytical test protocol that has permitted implementation of such a systems within an on-line real-time monitoring procedure with an acceptable degree of reliability.
Of even greater interest, however, is the capability of any such system to provide reliable testing results at effective time intervals. Past measuring techniques have proven effective on monthly or quarterly schedules; desired timeframes, however, are hourly, instead. The past analytical procedures, noted above, are rather difficult to employ at remote locations to begin with; to attempt testing every hour further exacerbates an already cumbersome procedure. On-line monitoring, though highly prized in the drinking water industry, has thus proven difficult to employ. Even with mobile methods in use, bench-top scale instruments have been necessary, rather than portable devices for such applications. Additionally, the reliability of any such on-line monitoring system has been highly suspect due to fluctuations in readings as calibration for short-term measuring intervals has not been easily incorporated therein, let alone actually followed.
Additionally, and to compound the difficulties associates with on-line monitoring systems of this type, the reliability of measurement and analysis of water samples is based upon the capability of the overall system to provide reproducible results at different times. With a standard sample provided for rather long periods of time until a new sample may be introduced within the remote system, the possibility that the standard has been altered through temperature fluctuations over time, or growth or production of undesirable organisms or chemical species therein during storage may cause problems ultimately in the resultant measurements. There thus exists a need to provide an effective remote calibration system in order to alleviate such potential analytical disparities. To date, there exists no reliable on-line continuous monitoring system for the type and amount of drinking water disinfection byproducts utilizing a calibration procedure at a remote location. Such a continuous system would basically involve testing procedures that are automatically undertaken remotely in regular intervals, whether by the hour, minute, day, etc. The ability to undertake remote testing and analysis permits on-line and real-time quantification and/or qualification of potential contaminants (i.e., total trihalomethane and haloacetic acid species) with little human involvement in the overall testing procedures thus provides significant efficiencies to such overall water sample testing capabilities. In order to provide reliable data in such remote locations, there is an expressed need to provide such effective calibration of the overall testing system in order to ensure the instrumentation is properly measuring specific levels, particularly at rather low concentrations. The capability of not only providing an on-line method for such contaminant analysis, but, as well, an overall calibrated system that functions remotely, too, would thus permit the greatest level of reliability possible on which a water utility or other like entity would base its water treatment activities, particularly when based upon water samples located within transfer lines, and not solely present in a laboratory. To date, although certain calibration methods have been accorded laboratory settings for certain liquid sample analytical processes, the ability to provide remote calibration protocols that render highly reliable measurements without human interaction or like involvement has not been provided the pertinent industries.